1. Technical Field
The present invention relates to over-coating compositions for a photoresist. More specifically, vertical and fine patterns can be obtained by using over-coating compositions containing acid-weakening materials even when light absorbance to a light source of photoresist is relatively high.
2. Background of the Related Art
In a process for manufacturing semiconductor fine circuits using KrF (248 nanometers (nm)), fine circuits of 150 nm L/S have already been formed, and patterns of less than 150 nm are currently required. Meanwhile, studies have been made on the fine circuit manufacturing process using light sources of low wavelength such as ArF (193 nm), F2 (157 nm), EUV (Extremely Ultraviolet; 13 nm). However, it is difficult to develop photoresist resins having excellent transmittance to these wavelengths. For example, photoresist resins used in I-line (365 nm) and KrF (248 nm) contain aromatic compounds and they cannot be used at 193 nm because its light absorbance to 193 nm is excessively high. As a result, photoresists for 193 nm wavelength have been introduced by using acrylic or alicylic resins, which do not include aromatic compounds. However, it is difficult to form good patterns by using these resins due to their high light absorbance to 193 nm.
FIG. 1a is a cross-sectional diagram of a photoresist pattern obtained when absorbance to a light source is low. Since the amount of light which reaches the upper portion and the lower portion of the photoresist film coated on a wafer is substantially the same, vertical patterns can be obtained. However, as shown in FIG. 1b, when absorbance to a light source is high, the amount of light which reaches the upper portion of the photoresist film is larger than that of the lower portion, thus the amount of acids generated from the upper portion is larger than that of the lower portion in the case of a chemical amplification type photoresist. Therefore, slant patterns after development may be formed as shown in FIG. 1b. That is, slant patterns are formed because the concentration gradient of acids generated by the light exposure is different depending on the height in a vertical direction.
In order to overcome the above-described problem, studies have been focused on developing resins having low light absorbance to a light source. However, the development of these resins reaches a limitation when light sources such as F2 (157 nm) or EUV (13 nm) are used.
A resist flow process or an alkali treatment process may be introduced to form patterns having fine sizes beyond exposure limitation. However, when the resist flow process is performed, the size of the first formed contact hole is not the same after the flow process, and is varied depending on the density and the size of the contact hole. The alkali treatment process causes deformation of the contact hole due to irregular diffusion of alkali compounds.